Summary:	ASTERISK-29267: H.263+ Format Attribute Module: not RFC 4629
Reporter:	Alexander Traud (traud)	Labels:	patch
Date Opened:	2021-01-28 08:26:45.000-0600	Date Closed:
Priority:	Minor	Regression?
Status:	Open/New	Components:	Resources/res_format_attr_h263
Versions:	13.38.1 16.16.0 18.2.0	Frequency of Occurrence
Related Issues:
Environment:		Attachments:	( 0) h263_upper.patch
Description:	Asterisk 11 introduced a format attribute module for H.263+. The idea is to pass the format parameters (line “fmtp” in SDP) from the originating call leg (caller) to the called leg (callee). The module is based on [RFC 4629|https://tools.ietf.org/html/rfc4629#section-8.1.1]. It parses all mentioned parameters and then generates one line “fmtp” again. However, there are bugs and limitations: # CPCF is simply missing   OK, nobody (?) is using that; forget about it. # CIFs are printed with MPI=0 when not specified   That is a violation because MPI can be 1 to 32 only. # K and N are printed with =0 when not specified   That is a violation because 0 is not a defined value. # BPP is printed with =0 when not specified   although 0 seems to have a meaning. # MaxBR is simply missing   OK, not specified RFC 4629, but some implementations use it. 2-5 can be solved by applying the same unset/nonzero approach as in the format attribute module for H.264. See the attached patch. However, however, RFC 4629 states: “Parameters offered first are the most preferred picture mode to be received.” This can be worked-around for the normal CIFs if one assumes that larger is better. In that case, the order of the CIFs in {{generate_sdp_fmtp(.)}} is simply reversed. See the attached patch. However, however, however, RFC 4629 includes that CPCF and allows CUSTOM. Those can be better or worse than other picture modes. This cannot be incorporated that easily. *Long story short* Saving the whole fmtp as one line, coping that over, rather than parsing and generating all parameters; wouldn’t that make much more sense?
Comments:	By: Asterisk Team (asteriskteam) 2021-01-28 08:26:46.817-0600 Thanks for creating a report! The issue has entered the triage process. That means the issue will wait in this status until a Bug Marshal has an opportunity to review the issue. Once the issue has been reviewed you will receive comments regarding the next steps towards resolution. Please note that log messages and other files should not be sent to the Sangoma Asterisk Team unless explicitly asked for. All files should be placed on this issue in a sanitized fashion as needed. A good first step is for you to review the [Asterisk Issue Guidelines|https://wiki.asterisk.org/wiki/display/AST/Asterisk+Issue+Guidelines] if you haven't already. The guidelines detail what is expected from an Asterisk issue report. Then, if you are submitting a patch, please review the [Patch Contribution Process|https://wiki.asterisk.org/wiki/display/AST/Patch+Contribution+Process]. Please note that once your issue enters an open state it has been accepted. As Asterisk is an open source project there is no guarantee or timeframe on when your issue will be looked into. If you need expedient resolution you will need to find and pay a suitable developer. Asking for an update on your issue will not yield any progress on it and will not result in a response. All updates are posted to the issue when they occur. Please note that by submitting data, code, or documentation to Sangoma through JIRA, you accept the Terms of Use present at [https://www.asterisk.org/terms-of-use/|https://www.asterisk.org/terms-of-use/]. By: Alexander Traud (traud) 2021-01-28 10:31:28.790-0600 Please, explain why the severity was lowered from major to minor. I do not know a workaround except to disallow H.263+ (or H.263) and allow H.264 instead. Beside the chance of lower quality video than possible, Asterisk should not make up parameters and definitely not generate/offer an invalid ‘a=fmtp’.